Oil separator for small particles

ABSTRACT

Device for separating oil mist from blow-by gases from an internal combustion engine, comprising a rotating cylindrical container ( 17 ) with a central inlet ( 23 ) for gases with oil mist at one end and a central outlet ( 24 ) for gases and peripheral outlets ( 25 ) for separated oil at the other end. Between the inlet and the outlet, narrow channels ( 34 ) extend in several layers, spaced from the axis of rotation, through which the gas with oil drops flows. Under the influence of the centrifugal force the drops of oil are moved at the same time radially, the rotational speed and the length and radial dimension of the channels being adapted to each other so that the oil drops strike the channel walls before flowing out of the channels.

BACKGROUND OF THE INVENTION

The present invention relates to a device for separating small drops ofliquid from a flowing gas containing liquid mist, comprising a firstcontainer, formed of a cylindrical lateral wall and two opposite endwalls, said first container having an inlet in one end wall for thegas/mist, a first outlet in its other end wall for the gas and a secondoutlet at or in the vicinity of the second end wall for liquid separatedout of the gas, a second container with means for rotatably mounting thefirst container in the second container rotationally symmetrically inrelation to said inlet and said first outlet, and drive means forrotation of the first container in the second container.

DESCRIPTION OF THE RELATED ART

It is a known fact that it is not possible to achieve piston ring sealsbetween the pistons and the surrounding cylinder walls of the cylindersin an internal combustion engine, which seal off the combustion chambers100% against the engine crankcase. A certain small amount of combustiongases, called here blow-by gas, thus always flows past the piston ringsand down into the engine crankcase. In order to prevent excessivepressure caused by the blow-by gas in the crankcase, the crankcase mustbe ventilated and the gas drawn off leaving only a low overpressure inthe crankcase.

Two types of crankcase ventilation are used, viz. either open or closedventilation. An engine with open ventilation can, quite simply, have adownwardly directed tube connected to the valve cover, for example, andwhich opens into the surrounding atmosphere. In an engine with closedcrankcase ventilation, the blow-by gases from the crankcase are led tothe engine intake conduit and are mixed with the intake air.

When evacuating blow-by gases, it has, up to now, been unavoidable thata certain amount of oil mist will accompany them. The amount of oilbeing carried with the gas depends on the placement of the ventilationoutlet and any filters or oil traps in the crankcase ventilation.Regardless of whether the engine has open or closed crankcaseventilation, it is desirable to keep the amount of oil in the evacuatedblow-by gas at a minimum. In the first case, it is to minimize theeffect on the environment and to keep the engine oil consumption at alow level. In the second case, it is to prevent oil deposits on or inthe components of the engine intake system, e.g. oil deposits on theimpeller blades of the compressor of a turbo-charged engine or oildeposits in the charge air cooler in engines with charge air cooling.

A number of different devices to separate oil from blow-by gases frominternal combustion engines are known. Among them are various types ofbaffle or screen systems, metal wire or textile fibre filters as well ascyclones and centrifuges. With the aid of baffle and screen systems, ithas up to now been possible to separate oil drops down to a diameter ofcirca 10 μm, with metal wire filters and cyclones down to circa 1.5 μmand with multi-layer textile fibre filters, e.g. fleece filters, down tocirca 0.4 μm. Baffle and screen systems have, in principle, an unlimitedlifetime and do not produce any pressure losses, but do not providesufficiently effective oil separation, since circa 80% of the oil massin the oil mist in the blow-by gases consists of oil drops with adiameter which is less than 1.5 μm. Previously known metal wire filtersand cyclones thus are not sufficient either for achieving effective oilseparation despite the fact that they have acceptable lifetimes andprovide limited pressure losses. Multi-layer fleece filters remain, butthese have limited lifetimes and therefore must be replaced often,leading to high costs. They also produce significant pressure losses.

SUMMARY OF THE INVENTION

The purpose of the present invention is to achieve a device of the typedescribed by way of introduction, i.e. a separator of centrifugal type,which is particularly, but not exclusively, intended for separation ofoil mist drops from blow-by gases from internal combustion engines andwhich can separate liquid drops of less than 1 μm without having thedisadvantage of a multi-layer fleece filter, for example.

This is achieved according to the invention by virtue of the fact thatthe inlet and the outlets communicate with each other via a plurality oflayers of peripherally spaced, narrow channels extending in thedirection of the rotational axis and being disposed at a radial distancefrom the rotational axis, said narrow channels having a radial dimensionbeing adapted to their length, their radial distance to the rotationalaxis, the flow velocity of the gas and the rotational speed, so that atleast the major portion of the liquid drops in the mist will have timeto be deposited on the channel walls before they reach the outlet.

Tests performed have demonstrated that in a preferred embodimentparticularly designed for separating oil mist from blow-by gases, with asuitable selection of the above-mentioned parameters, more than 90% ofall the oil mist in the gases was separated out. The gas velocity, thedistance which the oil drops must move radially outwards to strike thechannel wall, and the radial acceleration determine in this case therequired length of stay for the drops in the channels. This length ofstay determines in turn the required channel length. It has been shownthat the diameter (of circular channels) should not exceed, but shouldpreferably be less than 1 mm for the separator to have reasonabledimensions and a reasonable rotational speed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail below with reference toexamples shown in the accompanying drawings, where

FIG. 1 shows a schematic representation of an engine installation with adevice according to the invention,

FIG. 2 schematic longitudinal section through one embodiment of a deviceaccording to the invention, and

FIG. 3 is an enlarged cross-section along the line III—III in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

1 in FIG. 1 designates the engine block of a six-cylinder, four-strokediesel engine, and 2 designates a gearbox with clutch, coupled to theengine crankshaft. The engine is supercharged by a turbo compressor 3,which has a turbine 4 coupled to the engine exhaust manifold 5, and acompressor 6 coupled to the inlet manifold 7 via a charge air cooler 8.The suction side of the compressor 6 is coupled via an inlet conduit 9to an air filter 10.

In the crankcase of the engine 1, a screen separator 11 and a baffleseparator 12, known per se and only schematically indicated here, arearranged. A conduit 13 with a pressure regulator valve 14 and a pressuresensor 15 connect the engine crankcase with the inlet conduit 9 via anoil mist separator 16 according to the invention, which is shown in moredetail in FIG. 2.

The separator 16 comprises an inner container 17, which is formed of acylinder 18 and two end walls 19 and 20, each having a central openingin which a tubular shaft 21 and 22, respectively, is fixed. The interiorchannel 23 of the tubular shaft 21 forms an inlet for combustion gasesand oil mist, while the channel 24 of the tubular shaft 22 forms anoutlet for exhaust. Peripherally spaced openings 25 in the cylinder 18form outlets for separated-out oil. The tubular shafts 21, 22 aremounted in bearings 26, 27 of a stationary outer container 28, which hasa lower portion 29 forming a turbine housing. The lower tubular shaft 21extends through the turbine housing 29 and carries a turbine rotor 30.The housing 29 has an inlet 31 and an outlet 32 for oil from the enginelubrication system. When the engine is in operation and lubricant ispumped through the housing 29, the turbine rotor 30 drives the shaft 21so that the inner container 17 rotates in the outer container 28.

A cylindrical package 33 consisting of a plurality of layers of axialchannels 34 is fixed to the lateral wall 18 of the inner container 17.It is also possible to integrate the cylindrical lateral wall 18 in thechannel package 34. The channels 34 are open at their ends andcommunicate with radial passages 35, 36, which are defined between therespective end wall 19, 20, a pair of conical wall elements 37, 38 andintermediate, radially directed, peripherally evenly spaced intermediatewalls 39. An enlarged portion of a channel package 33 with ten layers isshown in cross section in FIG. 3. The channels 34 are greatly enlarged.In realistic tests with an inner container with a channel length ofcirca 200 mm, an inner container radius of circa 100 mm and a rotationalspeed of circa 3 000 rpm, the radial dimension “r” of the channelsshould be slightly less than 1 mm, in order for there to be enough timefor the smallest oil drops to strike the channel walls before the gaseshave flown out through the channels and out into the outlet passages 36.

In the example shown in FIG. 3, the channels 34 in the channel package33 are formed of alternating smooth and folded sheet metal cylinders 40and 41, respectively, i.e. corresponding to the construction ofcorrugated cardboard. The channel package can also have a solid body,e.g. a ceramic body with drilled or cast cylindrical channels. Theradial extent of the channel package amounts to approximately 20% of theradius of the first container. If the percentage is greater, there is arisk that the radially innermost channels will be so close to therotational axis that the centrifugal force on the smallest drops will betoo low to accelerate them out to the channel wall.

The oil, which is transported by the combustion gases through thechannels 34 and under the influence of the centrifugal force as theinner container rotates, strikes the channel walls, is ejected throughthe openings 25, as indicated by the solid arrows, and runs down intothe space between the containers to an outlet 42. From there the oil isled back to the engine crankcase. The combustion gases free of oil mistflow out through the upper tubular shaft 22, as indicated by the dashedarrow.

What is claimed is:
 1. Device for separating small drops of liquid froma flowing gas, containing liquid mist, comprising: a first container(17), formed of a cylindrical lateral wall (18) and two opposite endwalls (19, 20), said first container having an inlet (23) in one endwall for the gas/mist, a first outlet (24) in its other end wall for thegas and a second outlet (25) at or in the vicinity of the second endwall for liquid separated out of the gas, a second container (28) withmeans (26, 27) for rotatably mounting the first container in the secondcontainer rotationally symmetrically in relation to said inlet and saidfirst outlet, and drive means (30) for rotation of the first containerin the second container, wherein the inlet (23) and the outlets (24, 25)communicate with each other via a plurality of layers of peripherallyspaced, narrow channels (34) extending in the direction of therotational axis and being disposed at a radial distance from therotational axis, said narrow channels having a radial dimension (r)being adapted to their length, their radial distance to the rotationalaxis, the flow velocity of the gas and the rotational speed, so that atleast the major portion of the liquid drops in the mist will have timeto be deposited on the channel walls before they reach the outlet,characterized in that the inlet (23) of the first container (17) isjoined to a ventilation conduit from a crankcase of an internalcombustion engine (1), and its outlet (24) is joined to an inlet airconduit to the engine, and the inlet (23) has an inlet opening placedconcentrically with the rotational axis of the first container, saidinlet opening leading to a plurality of radial inlet passages (35)leading out to inlets of the channels (34), and that the channels haveoutlets opening, firstly, into a plurality of radial outlet passages(36), through which the gas can flow into an outlet opening (24) placedconcentrically with said rotational axis, and, secondly, into aplurality of outlet openings (25), through which liquid deposited underthe effect of the centrifugal force on the walls of the channels, canflow radially outwards to a space between the first container and thesecond container.
 2. Device according to claim 1, characterized in thatthe containers (17, 28) are oriented with the rotational axis verticalso that liquid separated out can flow, by the force of gravity, to theinlet end and out through a liquid outlet (42) from the second container(28).
 3. Device according to claim 1, characterized in that the endwalls have two axially spaced walls (19, 37 and 20, 38, respectively)which, together with intermediate radially directed wall portions (39),define said passages (35, 36).
 4. Device according to claim 1,characterized in that the drive means are formed by a liquid turbine(30).
 5. Device according to claim 4, characterized in that the endwalls (19, 20) are joined to rotatably mounted hollow shafts (21, 22),the interiors of which forming inlet and outlet channels, respectively(23 and 24, respectively), and in that a turbine wheel (30) is fixed toone of said shafts.
 6. Device according to claim 1, characterized inthat the extent of the channel layers radially amounts to circa 20% ofthe radius of the first container (17).
 7. Device according to claim 1,characterized in that the radius of the first container (17) is circa100 mm and its length circa 200 mm, that the container is designed to bedriven at a rotational speed of circa 3 000 rpm, that the radialdimension (r) of the channels (34) is less than 1 mm, and that theoutermost channel layer is located at a maximum radial distance from therotational axis.
 8. Device for separating small drops of liquid from aflowing gas, containing liquid mist, comprising: a first container (17),formed of a cylindrical lateral wall (18) and two opposite end walls(19, 20), said first container having an inlet (23) in one end wall forthe gas/mist, a first outlet (24) in its other end wall for the gas anda second outlet (25) at or in the vicinity of the second end wall forliquid separated out of the gas, a second container (28) with means (26,27) for rotatably mounting the first container in the second containerrotationally symmetrically in relation to said inlet and said firstoutlet, and drive means (30) for rotation of the first container in thesecond container, wherein the inlet (23) and the outlets (24, 25)communicate with each other via a plurality of layers of peripherallyspaced, narrow channels (34) extending in the direction of therotational axis and being disposed at a radial distance from therotational axis, said narrow channels having a radial dimension (r)being adapted to their length, their radial distance to the rotationalaxis, the flow velocity of the gas and the rotational speed, so that atleast the major portion of the liquid drops in the mist will have timeto be deposited on the channel walls before they reach the outlet,characterized in that the inlet (23) of the first container (17) isjoined to a ventilation conduit from a crankcase of an internalcombustion engine (1), and its outlet (24) is joined to an inlet airconduit to the engine, and the containers (17, 28) are oriented with therotational axis vertical so that liquid separated out can flow, by theforce of gravity, to the inlet end and out through a liquid outlet (42)from the second container (28).
 9. Device according to claim 8,characterized in that the end walls have two axially spaced walls (19,37 and 20, 38, respectively) which, together with intermediate radiallydirected wall portions (39), define said passages (35, 36).
 10. Deviceaccording to claim 9, characterized in that the inlet (23) has an inletopening placed concentrically with the rotational axis of the firstcontainer, said inlet opening leading to a plurality of radial inletpassages (35) leading out to inlets of the channels (34), and that thechannels have outlets opening, firstly, into a plurality of radialoutlet passages (36), through which the gas can flow into an outletopening (24) placed concentrically with said rotational axis, and,secondly, into a plurality of outlet openings (25), through which liquiddeposited under the effect of the centrifugal force on the walls of thechannels, can flow radially outwards to a space between the firstcontainer and the second container.
 11. Device according to claim 8,characterized in that the drive means are formed by a liquid turbine(30).
 12. Device according to claim 11, characterized in that the endwalls (19, 20) are joined to rotatably mounted hollow shafts (21, 22),the interiors of which forming inlet and outlet channels, respectively(23 and 24, respectively), and in that a turbine wheel (30) is fixed toone of said shafts.
 13. Device according to claim 8, characterized inthat the extent of the channel layers radially amounts to circa 20% ofthe radius of the first container (17).
 14. Device according to claim 8,characterized in that the radius of the first container (17) is circa100 mm and its length circa 200 mm, that the container is designed to bedriven at a rotational speed of circa 3 000 rpm, that the radialdimension (r) of the channels (34) is less than 1 mm, and that theoutermost channel layer is located at a maximum radial distance from therotational axis.
 15. Device for separating small drops of liquid from aflowing gas, containing liquid mist, comprising: a first container (17),formed of a cylindrical lateral wall (18) and two opposite end walls(19, 20), said first container having an inlet (23) in one end wall forthe gas/mist, a first outlet (24) in its other end wall for the gas anda second outlet (25) at or in the vicinity of the second end wall forliquid separated out of the gas, a second container (28) with means (26,27) for rotatably mounting the first container in the second containerrotationally symmetrically in relation to said inlet and said firstoutlet, and drive means (30) for rotation of the first container in thesecond container, wherein the inlet (23) and the outlets (24, 25)communicate with each other via a plurality of layers of peripherallyspaced, narrow channels (34) extending in the direction of therotational axis and being disposed at a radial distance from therotational axis, said narrow channels having a radial dimension (r)being adapted to their length, their radial distance to the rotationalaxis, the flow velocity of the gas and the rotational speed, so that atleast the major portion of the liquid drops in the mist will have timeto be deposited on the channel walls before they reach the outlet,characterized in that the inlet (23) of the first container (17) isjoined to a ventilation conduit from a crankcase of an internalcombustion engine (1), and its outlet (24) is joined to an inlet airconduit to the engine, and the inlet (23) has an inlet opening leadingto a plurality of radial inlet passages (35) leading out to inlets ofthe channels (34), and that the channels have outlet openings, firstly,into a plurality of radial outlet passages (36), through which the gascan flow into an outlet opening (24) placed concentrically with saidrotational axis.
 16. Device according to claim 15, characterized in thatthe containers (17, 28) are oriented with the rotational axis verticalso that liquid separated out can flow, by the force of gravity, to theinlet end and out through a liquid outlet (42) from the second container(28).
 17. Device according to claim 15, characterized in that the endwalls have two axially spaced walls (19, 37 and 20, 38, respectively)which, together with intermediate radially directed wall portions (39),define said passages (35, 36).
 18. Device according to claim 15,characterized in that the drive means are formed by a liquid turbine(30).
 19. Device according to claim 18, characterized in that the endwalls (19, 20) are joined to rotatably mounted hollow shafts (21, 22),the interiors of which forming inlet and outlet channels, respectively(23 and 24, respectively), and in that a turbine wheel (30) is fixed toone of said shafts.
 20. Device according to claim 15, characterized inthat the extent of the channel layers radially amounts to circa 20% ofthe radius of the first container (17).